The present invention concerns a method which allows for efficient serialized transmission of a handshake signal on a digital bus.
Wide parallel busses are often used to communicate large amounts of digital data at high speeds. Such busses have four basic groups of signal lines. These are control lines, data lines, handshake lines and timing lines. Parallel busses are usually bulky and their electrical properties usually limit the distance over which they can be built. It is impractical to operate such high speed busses over large distances due to the difficulty in matching propagation delays of multi-wire mediums and the costs and physical bulk of the cables.
One practical solution to extend the distance of a parallel bus is to convert the signals on the parallel bus into information which may be transported over a serial transmission medium using a single conductor. This is a cost effective solution which is limited primarily by the bandwidth of transmission medium and limitations of parallel to serial and serial to parallel conversion. Twisted pair wire, coaxial cable, RF and optical medium can be used to carry the signals. In the case of twisted pair wire and coaxial cable, the distance is limited by bandwidth and attenuation properties of the medium. In the case of fiber-optics, the distance is also limited by the signal to noise ratios and attenuation properties of optical to electrical interfaces. The fiber-optic medium is suitable for the longest distances due to its high frequency bandwidth and low attenuation.
Because of the above-described limitations, it is desirable to be able to send the maximum amount of information over the lowest possible bandwidth. This may be achieved by efficient coding techniques to convert the parallel bus binary data, timing and control information into a serial stream. Several layers of coding techniques are used to achieve this goal. In order to maximize the parallel to serial bandwidth ratio, techniques such as No Return to Zero, Invert on ones (NRZI) which transmits logical ones as transitions and zeroes as absence of transitions are utilized. 4B/5B, 5B/6B, 9B/10B and other coding techniques in conjunction with NRZI facilitate transmission of data and synchronization of clocks over a single transmission medium.